Engineering guide
The 2413 module calculates the wall thickness of seamless steel pipes and pipe bends under internal pressure to DIN 2413 Part 2, a German piping standard. The standard has been withdrawn; its content was merged into the consolidated DIN 2413, and piping within the scope of the Pressure Equipment Directive is today mostly calculated to DIN EN 13480-3, or to AD 2000 or EN 13445 for vessel tubes. For re-assessing existing lines, for spare part procurement and for retracing old designs, the withdrawn edition nevertheless remains relevant.
The core topic of the module is the pipe bend: when a pipe is bent, the stress distribution around the circumference changes – at the inner radius of the bend (intrados) the circumferential stress increases, at the outer radius (extrados) it decreases, while at the same time the wall thins on the outside and thickens on the inside. The standard captures this through factors depending on the relative bend radius R/D and the relative wall thickness, read from Figure 4 of the standard.
The module first determines the calculated wall thickness of the straight pipe from design pressure, design temperature and pipe size, and from it, using the factors for the inside and outside of the bend, the required wall thicknesses on both sides of the bend. This makes it possible to check whether the selected nominal wall thickness is still adequate at the intrados and extrados after bending.
Typical workflow
Define operating data and pipe size
Design pressure and design temperature are specified; nominal diameter and outside diameter fix the pipe size, and the nominal wall thickness is selected. The strength value of the pipe material at design temperature yields the allowable stress.
Calculate the wall thickness of the straight pipe
From pressure, outside diameter and allowable stress follows the calculated wall thickness of the straight pipe – the reference value to which the bend factors refer.
Describe the bend geometry
Bend type and diameter or radius of curvature are recorded and related to the pipe diameter (relative bend radius); likewise the relative nominal wall thickness is formed. Tight bends (small R/D) significantly increase the loading at the intrados.
Read the factors from Figure 4
For the inside and outside of the bend, the wall thickness factors are determined from Figure 4 of the standard as a function of relative bend radius and relative wall thickness.
Report the required wall thicknesses at the bend
The calculated wall thickness of the straight pipe is converted with the factors to the intrados and extrados. The actual wall thickness after bending – thickened on the inside, thinned on the outside – must reach the respective calculated wall thickness plus allowances.
Frequently asked questions
Which standard replaces DIN 2413 Part 2 today?
The parts of DIN 2413 were merged, and piping design has migrated to the European codes: for industrial piping, DIN EN 13480-3 applies with its own rules for pipe bends, and in the pressure vessel field AD 2000 or EN 13445. Existing lines designed to DIN 2413 may continue to be evaluated on their original design basis.
Why does the inner radius of a bend need more wall thickness even though the wall becomes thicker there during bending?
At the intrados the circumferential stress due to internal pressure is highest because of the torus geometry – the factor there is greater than 1. Against this stands the wall thickening during bending. The check therefore compares, on each side of the bend, the wall thickness actually present after bending with the wall thickness required there; whether thickening and increased demand offset each other depends on the bending process and the bend radius.
What must be considered regarding wall thinning at the outer radius of the bend?
During hot and cold bending the wall at the extrados thins by typically 5 to 15% depending on the process, more for tight radii. The required nominal wall thickness of the starting pipe must be chosen so that after thinning, the calculated wall thickness of the outer side plus corrosion and tolerance allowances remains – otherwise a pipe of the next heavier wall thickness series must be used.
Does the calculation also apply to welded pipes and to bends containing a weld seam?
DIN 2413 Part 2, as implemented here, covers seamless steel pipes. For welded pipes the weld joint factor must additionally be taken into account, and the position of the seam in the bend (neutral axis, intrados, extrados) influences the check. For such cases the provisions of the successor standards (e.g. EN 13480-3) should be used.
Technical content source: LV-Solved-Problems-Content 628d313247e7